Cooling device and air flow control method

Abstract

To provide a cooling device with high cooling efficiency capable of restraining power consumption of a plasma actuator.SOLUTION: A cooling device according to the present invention comprises: a heat sink in which plural fins stand on a base plate to form a flow path between the fins; a plasma actuator provided on the fin and generating an induction air flow in a longitudinal direction of the flow path by applying an alternating-current voltage; and a control device for burst-driving the plasma actuator. The control device changes a driving voltage and / or a driving frequency according to a change of a request cooling amount to change a volume power of the plasma actuator, and changes a duty ratio and / or a burst frequency of burst-driving according to the volume power. Therefore, the cooling device with restrained power consumption of the plasma actuator and with high cooling efficiency can be provided.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cooling device and an air flow control method, and more particularly to a cooling device including a heat sink and a plasma actuator, and a method for controlling an air flow flowing in a flow path of the heat sink.

Background Art

[0002] Power conversion devices such as converters include electronic components that generate heat, such as semiconductors, capacitors, and coils, and a heat sink is attached to cool these electronic components.

[0003] In recent years, miniaturization and high power of power conversion devices have been required. When electronic components are arranged densely for miniaturization, the density of heat-generating elements in the power conversion device increases. In addition, the amount of heat generated by the heat-generating elements increases due to high power, so it is necessary to improve the performance of the heat sink for cooling these.

[0004] Patent Document 1 describes a cooling device that intermittently generates an induced flow from a plasma actuator provided in a heat sink to generate a vortex flow on the heat sink surface.

[0005] And, by changing the fundamental frequency for driving the plasma actuator and the duty ratio of burst driving, and changing the amount of electric power applied to the plasma actuator, the speed of the generated induced flow can be changed, and it is disclosed that the heat transfer rate from the heat-generating body can be improved.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the cooling device described in Patent Document 1, the driving frequency of the alternating voltage applied to the plasma actuator and the duty ratio of the burst drive are each changed independently, and the power applied to the plasma actuator is not changed by changing the combination thereof. Therefore, the cooling efficiency with respect to the power consumption of the plasma actuator is low.

[0008] The present invention has been made in view of such problems of the prior art, and an object thereof is to provide a cooling device having high cooling efficiency capable of suppressing the power consumption of a plasma actuator.

Means for Solving the Problems

[0009] As a result of intensive studies to achieve the above object, the present inventor has found that when the plasma actuator is driven in bursts, the duty ratio and burst frequency of the burst drive, which have high cooling efficiency with respect to power consumption, are not constant but change depending on the body force of the plasma actuator, and has completed the present invention.

[0010] That is, the cooling device of the present invention includes a heat sink in which a plurality of fins are erected on a base plate and a flow path is formed between the fins, a plasma actuator provided on the fins for generating an induced air flow in the length direction of the flow path by applying an alternating voltage, and a control device for driving the plasma actuator in bursts. And the control device is characterized in that it changes the driving voltage and / or driving frequency in accordance with a change in the required cooling amount to change the body force of the plasma actuator, and changes the duty ratio and / or burst frequency of the burst drive in accordance with the body force.

[0011] In addition, the air flow control method of the present invention is a method for controlling the air flow in a flow path formed between the fins of a heat sink in which a plurality of fins are erected on a base plate. Then, the plasma actuator provided on the fin is driven in bursts to generate an induced air flow in the flow path, and the driving voltage and / or the driving frequency are changed according to a change in the required cooling capacity to change the body force of the plasma actuator, and the duty ratio and / or the burst frequency of the burst driving are changed according to the body force.

Effect of the Invention

[0012] According to the present invention, since the duty ratio and / or the burst frequency of the burst driving are changed according to a change in the body force of the plasma actuator, it is possible to provide a cooling device with high cooling efficiency that suppresses the power consumption of the plasma actuator.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0014] The cooling device of the present invention will be described in detail. The cooling device of the present invention includes a heat sink, a plasma actuator, and a control device that drives the plasma actuator, and optionally has a fan that generates a main flow.

[0015] As shown in FIG. 1, the heat sink H has a plurality of fins 2 erected on one main surface of the base plate 1, and a flow path 3 is formed between the fins. Also, a heat generating body (cooled body) A is in contact with the other main surface of the base plate 1 to promote heat dissipation of the heat generating body.

[0016] In FIG. 1, the X-axis direction is the length direction of the flow path and the flow direction of the air flow. The Y-axis direction is the width direction of the flow path, and the Z-axis direction is the height direction of the flow path.

[0017] As shown in FIG. 2, the plasma actuator P has a coated electrode 12 and an exposed electrode 11 separated by a dielectric 10 and arranged offset in the in-plane direction of the main surface of the dielectric. Then, by applying an alternating voltage between the electrodes, a barrier discharge 14 occurs, and an induced flow F is generated in the in-plane direction of the main surface of the dielectric 10.

[0018] This plasma actuator 1 is provided on the fins of the heat sink 2 so that an induced air flow is generated in the length direction (X direction) of the flow path.

[0019] As shown in FIG. 3, the control device applies an alternating voltage between the electrodes of the plasma actuator 1 via a power conversion circuit to generate an induced flow.

[0020] Here, as shown in FIG. 4, the plasma actuator discharges at the vicinity of the peak voltage of the applied alternating voltage by applying a sine wave high voltage of about 10 to 20 kHz to generate an induced flow. In the present invention, the frequency of the alternating voltage for generating this induced flow is called the "driving frequency", and the voltage is called the "driving voltage".

[0021] Also, as shown in FIG. 4, the cooling device of the present invention performs burst driving in which the alternating voltage is intermittently applied to the plasma actuator to intermittently generate an induced flow. In the present invention, the cycle of On / Off of the alternating voltage when the induced flow is intermittently generated as described above is called the "burst frequency", and the time ratio of On is called the "duty ratio".

[0022] By increasing the driving voltage and driving frequency, the barrier discharge in the plasma actuator becomes larger, the body force becomes larger, and a strong induced flow is generated, thereby improving the cooling capacity.

[0023] The control device changes the driving voltage and driving frequency according to the cooling requirement signal received from a temperature sensor provided on the heat sink, a heating element, etc., thereby changing the body force of the plasma actuator and changing the cooling capacity of the cooling device.

[0024] Therefore, it is possible to prevent overcooling of the heating element and save waste of power consumed for cooling.

[0025] The induced flow generated by the plasma actuator has a slower flow velocity near the fins due to friction with the fins, so the flow velocity is different in the thickness direction of the induced flow, that is, in the width direction (Y direction) of the flow path. In addition, when burst driving is performed, an induced flow is generated when the AC voltage is On and stops when it is Off, so a pressure difference occurs in the flow direction (X direction) of the induced flow, and a flow in the direction opposite to the induced flow is generated to form a vortex.

[0026] The size of this vortex can be changed by the burst frequency. By increasing the burst frequency, small vortices are formed, and by decreasing the burst frequency, large vortices are formed.

[0027] When the size of the vortex changes, the influence of the vortex on the boundary layer near the fins also changes. Therefore, even if the driving voltage and driving frequency applied to the plasma actuator are the same, that is, the body force is the same, the cooling capacity of the cooling device changes depending on the burst frequency.

[0028] In addition, due to the viscosity of the gas, there is a time lag until the induced flow is sufficiently accelerated after the AC voltage is turned on.

[0029] Therefore, when the AC voltage is turned off before the induced flow is sufficiently accelerated by burst driving, the induced flow is not sufficiently accelerated, so even if the body force of the plasma actuator is the same, the flow rate of the induced flow decreases.

[0030] And when the flow rate of the induced flow changes, the shape of the vortex formed due to the change in the influence received from the friction with the fins changes. Therefore, even if the body force is the same as the burst frequency, the cooling capacity of the cooling device changes depending on the duty ratio.

[0031] And the influence of the burst frequency on the size of the vortex and the influence of the duty ratio on the flow rate of the induced flow change depending on the force that the plasma actuator generates the induced flow, that is, the body force. Therefore, the burst frequency and duty ratio that can maximize the cooling capacity of the cooling device are not constant and change depending on the body force of the plasma actuator.

[0032] The cooling device of the present invention not only changes the body force of the plasma actuator according to the cooling requirement signal, but also changes the burst frequency and duty ratio, so the range of change in cooling capacity can be widened.

[0033] It is preferable that the control device makes the duty ratio and burst frequency of the burst driving follow the optimal operating point that can maximize the cooling efficiency at the body force corresponding to the required cooling amount. The optimal operating point is stored in the control device in advance.

[0034] As a result, even if the required cooling amount changes, the cooling capacity at that body force is always maximized, so it is possible to minimize the power consumption of the plasma actuator.

[0035] The cooling device of the present invention can include a fan that causes a main air flow to flow in the flow path. The main air flow from the fan flows in the same direction as the induced flow in the length direction of the flow path, so that the cooling capacity can be improved in combination with the induced flow.

[0036] As the above fan, an axial flow fan or a blower fan (centrifugal fan) can be used.

Example

[0037] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

[0038] [Example] A plasma actuator was provided at a position 19 mm from the upstream end of an aluminum heat sink having a straight flow path with a flow path length of 75 mm and a flow path width of 5 mm as shown in FIG. 5, and the main air flow was passed from the upstream fan, and the above plasma actuator was driven in burst mode.

[0039] The driving voltage and driving frequency were changed to change the body force of the plasma actuator, and for each of the body forces, the driving duty ratio and burst frequency were changed to measure the Nusselt number in the width direction (Y direction) of the flow path.

[0040] The Nusselt number is the ratio of the heat conduction to the heat transfer of the convecting fluid, and the larger the Nusselt number, the higher the heat transport effect by convection. Also, a duty ratio of 0 means no driving of the plasma actuator, and a duty ratio of 95 means that the on-time per unit time is 95% and the off-time is 5%.

[0041]

Table 1

[0042] From the results in Table 1, as the body force of the plasma actuator decreases, the duty ratio with the highest cooling capacity shifts to a smaller value, and the burst frequency with the highest cooling capacity also changes. Therefore, it can be seen that the optimal operating points of the duty ratio and burst frequency with the highest cooling capacity change depending on the body force of the plasma actuator. It can be understood that not only can the volume force of the plasma actuator be changed, but also the duty ratio and burst frequency of the burst drive can be made to follow the optimal operating point of the volume force at that time, further reducing power consumption.

Explanation of symbols

[0043] H Heat sink 1 Base plate 2 Fin 3 Flow path P Plasma actuator 10 Dielectric 11 Exposed electrode 12 Coated electrode 13 AC power supply 14 Barrier discharge F Induced air flow C Control device A Heating element

Claims

1. A heat sink having a plurality of fins erected on a base plate and forming a flow path between the fins, a plasma actuator provided on the fins and generating an induced airflow in the length direction of the flow path by applying an alternating voltage, and a control device for burst-driving the plasma actuator, the cooling device comprising: The control device changes the driving voltage and / or the driving frequency according to a change in the required cooling capacity to change the body force of the plasma actuator, and changes the duty ratio and / or the burst frequency of the burst driving according to the body force. A cooling device characterized by the above.

2. The cooling device according to claim 1, wherein the control device causes the duty ratio of the burst driving to follow an optimum operating point corresponding to the body force.

3. The cooling device according to claim 1 or 2, wherein the control device causes the burst frequency of the burst driving to follow an optimum operating point corresponding to the body force.

4. Furthermore, it includes a fan that flows a main airflow in the flow path, The cooling device according to claim 1, wherein the main airflow flows in the length direction of the flow path.

5. A method for controlling the airflow in a flow path formed between the fins of a heat sink having a plurality of fins erected on a base plate, burst-driving a plasma actuator provided on the fins to generate an induced airflow in the flow path, changing the driving voltage and / or the driving frequency according to a change in the required cooling capacity to change the body force of the plasma actuator, and changing the duty ratio and / or the burst frequency of the burst driving according to the body force. An airflow control method characterized by the above.

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